US7198510B2 - Kelvin connector for a battery post - Google Patents

Abstract

A Kelvin connector for coupling to a post of a battery includes a first contact having a surface which at least partially conforms to and is adapted to engage and electrically connect to a surface of the post. The connector also includes a second contact having a surface which at least partially conforms to and is adapted to engage and electrically connect to the surface of the post. An electrical insulator between the first contact and the second contact urges the surface of the first contact and the surface of the second contact against the surface of the post and thereby forms a Kelvin connection to the post.

Description

BACKGROUND OF THE INVENTION

The present invention generally relates to storage batteries. More specifically, the present invention relates to a Kelvin connector for engaging a battery post.

Storage batteries, such as lead acid storage batteries of the type used in the automotive industry, have existed for many years. However, understanding the nature of such storage batteries, how such storage batteries operate and how to accurately test such batteries has been an ongoing endeavor and has proved quite difficult. Storage batteries consist of a plurality of individual storage cells electrically connected in series. Typically, each cell has a voltage potential of about 2.1 volts. By connecting the cells in series, the voltage of the individual cells are added in a cumulative manner. For example, in a typical automotive storage battery, six storage cells are used to provide a total voltage when the battery is fully charged up to 12.6 volts.

Several techniques have been used to test the condition of storage batteries. These techniques include a voltage test to determine if the battery voltage is below a certain threshold, and a load test that involves discharging a battery using a known load. A more recent technique involves measuring the conductance of the storage batteries. This technique typically involves the use of Kelvin connections for the testing equipment. A Kelvin connection is a four point connection technique that allows current to be injected into a battery through a first pair of connectors attached to the battery posts, while a second pair of connectors is attached to the battery posts in order to measure the voltage across the posts. Typically, a pair of pivoting jaw-type battery clamps are respectively clamped to the battery posts and are designed to continue the circuit that includes the Kelvin connection. The jaws of each clamp are electrically isolated from each other. Pivoting jaw-type clamps provide tenuous mechanical and electrical connections to the battery contacts and could easily inadvertently fall off. Thus, pivoting jaw-type battery clamps are usually suitable only for temporarily connecting test equipment to battery contacts. Pivoting jaw-type clamps are not suitable for use with test modules that are integrated with the storage batteries and require relatively permanent connections to the battery posts.

SUMMARY OF THE INVENTION

A Kelvin connector for coupling to a post of a battery includes a first contact having a surface which at least partially conforms to and is adapted to engage and electrically connect to a surface of the post. The connector also includes a second contact having a surface which at least partially conforms to and is adapted to engage and electrically connect to the surface of the post. An electrical insulator between the first contact and the second contact urges the surface of the first contact and the surface of the second contact against the surface of the post and thereby forms a Kelvin connection to the post.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 to 3 illustrate simplified block diagrams of Kelvin connector s in accordance with embodiments of the present invention.

FIGS. 4 to 6 illustrate simplified block diagrams of a method of forming a Kelvin connector in accordance with an embodiment of the present invention.

FIGS. 7 and 8 illustrate simplified block diagrams of batteries with integrated testers employing Kelvin connector s in accordance with embodiments of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates a top plan view of a Kelvinconnector100 in accordance with an embodiment of the present invention. The same reference numerals are used in the various figures to represent the same or similar elements. Kelvinconnector100 is designed to engage abattery post101, and to electrically couple two external electrical conductors (not shown), such as conductors of a Kelvin connection, to thebattery post101. Kelvinconnector100 is designed for use on a smooth wall battery post, although it could easily be adapted for use with other kinds of posts, such as, for example, a threaded battery post.

As can be seen inFIG. 1, Kelvinconnector100 includes a pair of substantially identical opposing electrical contacts102 (contacts facing each other) mechanically connected together but electrically insulated from one another by means of aninsulator104 that has acentral opening105. Eachcontact102 includes aninsulator support portion106 and apost grasping portion108. Eachinsulator support portion106 ofcontacts102 is embedded within theinsulator104. Eachpost grasping portion108 extends inwardly from theinsulator support portion106 into thecentral opening105 ofinsulator104 and engagesbattery post101 throughsurfaces109. A pair ofconnection bars110 that extend outwardly fromcontacts102 andinsulator104 facilitate the connection of external circuitry tocontacts102.Connection bars110 include connection grooves112 that hold ends of external electrical conductors. The ends of external electrical conductors may be soldered toconnection bars110.

In general, eachelectrical contact102 may be formed from any electrically conductive sheet metal. Preferably,electrical contacts102 are formed from copper and solder plated before formation of Kelvinconnector100.Insulator104 may be made of any suitable electrically insulative material such as plastic or composite material.

The opening formed by post graspingportions108 of theopposing contacts102 is sized to form a tight fit with thebattery post101. The opening105 ininsulator104 is larger in diameter than the opening between graspingportions108 andbattery post101 so as to have a substantial annular space betweeninsulator104 and the peripheral surface ofbattery post101. Once Kelvinconnector100 is positioned overbattery post101, force is applied onconnector100 in a downward direction using, for example, a pipe having a bore that is substantially equal to the diameter of theopening105 ininsulator104. Thus, Kelvinconnector100 is forced ontobattery post101 such thatelectrical contacts102 are in tightly gripping engagement withbattery post101, thereby providing good electrical contact between post graspingportions108 ofelectrical contacts102 andbattery post101. Kelvin connectors, such as100, are sized according to battery post diameters. Thus, a Kelvin connector for a positive post usually has a larger diameter than a Kelvin connector for a negative post since the positive battery post is typically larger in diameter than the negative battery post.

FIG. 2 illustrates a Kelvinconnector200 in accordance with another embodiment of the present invention. As can be seen inFIG. 2,insulator support portions106 ofelectrical contacts102 include a plurality ofgrooves202, which are included to provide better coupling betweeninsulator104 andelectrical contacts102. The remaining elements of Kelvinconnector200 are similar to the elements of Kelvinconnector100 ofFIG. 1. As in the case of Kelvin connector100 (FIG. 1) described above, insulator supportportions106 of Kelvinconnector200 are also embedded withininsulator104. However, in Kelvinconnector200, portions ofinsulator104 extend throughgrooves202, thereby providing additional mechanical coupling betweeninsulator104 andelectrical contacts102. The coupling occurs during the formation of Kelvinconnector200 whereininsulator104 flows aroundgrooves202 and subsequently solidifies to form a strong mechanical bond withcontacts102.

FIG. 3 illustrates a Kelvinconnector300 in accordance with another embodiment of the present invention. As can be seen inFIG. 3, post graspingportions108 ofelectrical contacts102 include a plurality of teeth orprongs302, which are employed to gripbattery post101 instead of post graspingportions108 with smooth contours shown inFIGS. 1 and 2. The remaining elements of Kelvinconnector300 are similar to the elements of Kelvin connector s100 and200 (FIGS. 1 and 2) and function as described above. Teeth302 help resist axial removal ofconnector300 frompost101 in a manner similar to a “Chinese finger trap”.Teeth302 also prevent slipping, thereby insuring proper electrical connection betweenelectrical contacts102 andbattery post101.Teeth302 are shown disposed substantially in a common plane, but may extend, together or separately, in any number of different non-planer directions and may be of different shapes.

FIGS. 4,5 and6 collectively illustrate a method of forming a Kelvin connector in accordance with an embodiment of the present invention. The method includes providing an electrically conductive piece which is illustrated inFIG. 4.Conductive piece400 includes a pair of opposingelectrical contacts102 coupled together by shortingbars402. Eachcontact102 includes aninsulator support portion106 and apost grasping portion108. Eachinsulator support portion106 includes a plurality ofgrooves202 and eachpost grasping portion108 includes a plurality ofteeth302.Contacts102 also include connection bars110 with connection grooves112.Insulator104 is formed oversupport portions106 ofelectrical contacts102 such thatinsulator104 extends throughgrooves202. InFIG. 5,conductive piece400 is shown with support portions ofcontacts102 embedded withininsulator104 after the insulator-formation process is complete. As can be seen inFIG. 5,insulator104 is formed such that mechanical coupling betweencontacts102 is provided. After formation ofinsulator104, shortingbars402 are removed fromconductive piece400 to electrically isolatecontacts102 from each other.FIG. 6 shows Kelvin connector600 formed by the method described above. As can be seen inFIG. 6,contacts102 remain mechanically coupled together byinsulator104 after removal of shorting bars402.

Embodiments of the present invention, described above, are particularly useful with a storage battery having an integrated battery test module for performing a battery test on electrical cells of the storage battery. As used herein “integrated” can include a separate battery test module which is attached to the battery housing. Integrated battery testers employing Kelvin connector s to couple a Kelvin connection to battery posts in accordance with the present invention are described below in connection withFIGS. 7 and 8.

FIG. 7 is a top plan view of battery with an integrated tester with which the present invention is useful. As illustrated inFIG. 7, theintegrated system700 includes abattery702 withposts704 and706 and atest module708 mounted to the battery housing. A four point or Kelvin connection technique is used to couplebattery test module708 tobattery702.Kelvin connections710 and712 are used to couple tobattery posts704 and706, respectively, ofbattery702.Kelvin connection710 includes twoindividual connections710A and710B. Similarly,Kelvin connection712 includes two individual connections,712A and712B.Post grasping devices714 and716 firmly grip battery posts704 and706 and couple them toelectrical connections710 and712.Post grasping devices714 and716 are Kelvin connector s (such as100,200,300 and600) of the present invention, described above.Battery test module708 includes anoptional input718 andoptional outputs720 and722. Input718 can be, for example, a push button or other input which can be actuated by an operator.Output720 can be, for example, an LED or other type of visual indicator which provides a pass/fail indication of a battery test.Output720 can also be in the form of a series of outputs which can comprise LEDs. In other aspects,output722 can be used to send data, using any appropriate technique, to a remote computer or monitoring system.Output722 can be used to provide a quantitative output of a battery test.

FIG. 8 is a simplified circuit diagram oftest module708.Module708 is shown coupled tobattery702.Module708 operates in accordance with one embodiment of the present invention and determines the conductance (G_BAT) ofbattery702 and the voltage potential (V_BAT) betweenposts704 and706.Module708 includescurrent source800,differential amplifier802, analog-to-digital converter804 andmicroprocessor806.Amplifier802 is capacitively coupled tobattery702 through capacitors C₁, and C₂. Amplifier802 has an output connected to an input of analog-to-digital converter804.Microprocessor806 is connected tosystem clock808,memory810,visual output812 and analog-to-digital converter804.Microprocessor806 is also capable of receiving an input frominput device816. Further, an input/output (I/O)port817 is provided.

In operation,current source800 is controlled bymicroprocessor806 and provides a current in the direction shown by the arrow inFIG. 8. In one embodiment, this is a square wave or a pulse.Differential amplifier802 is connected toposts704 and706 ofbattery702 through capacitors C₁and C₂, respectively, and provides an output related to the voltage potential difference betweenposts704 and706. In a preferred embodiment,amplifier802 has a high input impedance.Circuitry708 includesdifferential amplifier820 having inverting and noninverting inputs connected toposts704 and706, respectively.Amplifier820 is connected to measure the open circuit potential voltage (V_BAT) ofbattery702 betweenposts704 and706. The output ofamplifier820 is provided to analog-to-digital converter804 such that the voltage acrossposts704 and706 can be measured bymicroprocessor806.

As described above,module708 is connected tobattery702 through a four-point connection technique known as a Kelvin connection. This Kelvin connection allows current I to be injected intobattery702 through a first pair of posts while the voltage V across theposts704 and706 is measured by a second pair of connections. Because very little current flows throughamplifier802, the voltage drop across the inputs toamplifier802 is substantially identical to the voltage drop acrossposts704 and706 ofbattery702. The output ofdifferential amplifier802 is converted to a digital format and is provided tomicroprocessor806.Microprocessor806 operates at a frequency determined bysystem clock808 and in accordance with programming instructions stored inmemory810.

Microprocessor806 determines the conductance ofbattery702 by applying a current pulse I usingcurrent source800. The microprocessor determines the change in battery voltage due to the current pulse I usingamplifier802 and analog-to-digital converter804. The value of current I generated bycurrent source800 is known and is stored inmemory810. In one embodiment, current I is obtained by applying a load tobattery702.Microprocessor806 calculates the conductance ofbattery702 using the following equation:

$\begin{array}{cc}\mathrm{Conductance}=G_{\mathrm{BAT}}=\frac{\Delta I}{\Delta V}& \mathrm{Equation}1\end{array}$
where ΔI is the change in current flowing throughbattery702 due tocurrent source800 and ΔV is the change in battery voltage due to applied current ΔI. Atemperature sensor818 can be thermally coupled tobattery702 and used to compensate battery measurements. Temperature readings can be stored inmemory810 for later retrieval.

Battery test module708 may be built intobattery702 or mounted onbattery702 any time after it is built and coupled tobattery posts704 and706 using Kelvin connector s714 and716 of the present invention.

Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention. Embodiments of the Kelvin connector of the present invention can be used to couple different electrical circuits to battery posts other than the tester circuits described above. In addition, although the electrical contacts of the Kelvin connector are shown as opposing each other inFIGS. 1 through 8, the electrical contacts may be positioned in any orientation without departing from the spirit and scope of the invention.

Claims (7)

What is claimed is:

1. A Kelvin connector for coupling to a post of a battery, comprising:

a first contact having a surface which at least partially conforms to and is adapted to engage and electrically connect to a surface of such post;

a second contact having a surface which at least partially conforms to and is adapted to engage and electrically connect to the surface of such post; and

an electrical insulator between, and at least partially overmolded on, the first contact and the second contact to define an alignment plane that is substantially transverse to such post, to mechanically connect the contacts together and to align the surface of the first contact and the surface of the second contact against the surface of such post and thereby form a Kelvin connection to such post, wherein the first contact, the second contact and the insulator form a closed loop that is used to encircle such battery post; and

wherein the first contact and the second contact are substantially horizontally opposed to each other within the alignment plane.

2. The apparatus ofclaim 1 wherein the first contact comprises:

an insulator support portion which is embedded within the electrical insulator; and

a post grasping portion on which the surface of the first contact resides.

3. The apparatus ofclaim 1 further comprising a first connection bar integral with the first electrical contact and a second connection bar integral with the second electrical contact.

4. The apparatus ofclaim 1 wherein the first electrical contact and the second electrical contact are formed from electrically conductive sheet metal.

5. The apparatus ofclaim 1 wherein the first electrical contact and the second electrical contact are copper pieces with solder plating.

6. The apparatus ofclaim 1 wherein the insulator comprises plastic.

7. The apparatus ofclaim 1 wherein the insulator comprises a composite material.

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